Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
1999-03-11
2001-05-08
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas of combustion
C073S001060, C324S615000, C123S674000, C123S703000
Reexamination Certificate
active
06227033
ABSTRACT:
TECHNICAL FIELD
This invention relates to an automotive engine fuel control including a wide range oxygen sensor in the exhaust gas stream, and more particularly a control method for using an auxiliary switching oxygen sensor to automatically calibrate the wide range oxygen sensor.
BACKGROUND OF THE INVENTION
Effective emission control of internal combustion engine exhaust gases with a catalytic converter requires precise control of the air/fuel ratio supplied to the engine cylinders. For this purpose, it is customary to install an oxygen sensor in the engine exhaust pipe, and to use the sensor output as a feedback signal for closed-loop fuel control.
In general, two different types of oxygen sensors are available for usage in automotive fuel control. The most common and least expensive sensor, referred to as a switching sensor, has a bi-stable output voltage that switches or toggles between first and second states corresponding to lean and rich conditions of the sensed exhaust gas, relative to a stoichiometric air/fuel ratio of approximately 14.7:1 for pump gasoline. The other type of oxygen sensor, referred to as a universal exhaust gas oxygen sensor, or wide-range oxygen sensor, has an analog output that varies in amplitude in relation to the deviation of the sensed exhaust gas from the stoichiometric air/fuel ratio. Of the two sensor types, the switching sensor is less expensive but provides limited information, whereas the wide-range sensor enables improved fuel control performance.
A portion of cost of the wide-range sensor is related to calibration; typically, the calibration is performed off-line by the sensor manufacturer, and active or passive elements in the sensor wiring harness are selected or programmed to provide a standard output voltage vs. air/fuel ratio transfer function. A related disadvantage of the wide-range sensor is that the sensor characteristics may tend to drift with age and/or other factors, leading to fuel control errors since the one-time calibration cannot account for the drift.
SUMMARY OF THE INVENTION
The present invention is directed to an improved fuel control in which the transfer function of a wide-range exhaust gas oxygen sensor is automatically and periodically learned or calibrated in the course of vehicle operation. The auto-calibration method reduces the sensor cost to enable high performance fuel control at a lower cost, and periodically updates the calibration so that the improved performance can be achieved in spite of sensor drift due to age or other factors.
According to the invention, the engine fuel control is based on the output of a wide range oxygen sensor, which is automatically and periodically calibrated at two different operating conditions. The first operating condition occurs during steady state operation when a switching sensor disposed in the exhaust gas stream downstream of the catalytic converter indicates that the engine is being fueled at the stoichiometric air/fuel ratio. The second operating condition occurs either during vehicle deceleration when engine fueling is cut off or when the engine is turned off. The wide range sensor voltage developed under the first operating condition is stored as a stoichiometry calibration, and the wide range sensor voltage developed under the second operating condition is stored as a “free air” calibration. Once both calibration points have been determined, the transfer function of the wide range sensor is adjusted to match the stored voltages, and engine fueling is thereafter based on the adjusted transfer function. In a first embodiment, a characteristic transfer function stored in the controller in the form of a mathematical model or look-up table is shifted so as to intersect, as nearly as possible, the two determined calibration points. In a second embodiment, the controller effectively re-constructs the transfer function by incrementally adjusting the engine fueling with respect to the determined calibration points, and recording the corresponding sensor output voltages.
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Cichosz Vincent A.
Delphi Technologies Inc.
Wiggins David J.
Williams Hezron
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